Method of working open-hearth furnaces and the like



July 14, 1925 A. L. FEILD 1 uaruon opwonxme OPEN HE'AR'II'H FURNACES AND THE LIKE Filed April 29. 1324 o m w MMUWM Q mm /4 W mm M a wa. a

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' Patented July 14, 1925;

. UNITED STATES ALEXANDER L.

PATENT OFFICE.

AIR PRQDUCTS COMPANY, A CORPORATION OF OHIO.

daemon on wonxmo ornn-nnmrn Furnaces AND THE LIKE.

Application filed April 29, 1924. Serial No. 709,000.

To all whom it may concern:

Be it known that I, AmaxANona L. Farm, a citizen of the United States, residing at Jackson Heights, in the, county of Queens and State of New York, have invented certain new and useful Improvements in Methods of Working Open-Hearth Furnaces t has long been realized that the open hearth process could be operated much more efliciently by increasing the temperature of the flame playing upon the charge. Increase of temperaturemay readily be obtained by supplylng oxygen or oxygen-enriched. .air, instead of atmospheric am In practice, however, such processes are recluded, because there is no available ref? can sustain the heat so generated.

The roof of the furnace is subjected to the severest conditions. Silica brick,.the best available refractory at the present time, is

heated almost to the point of failure by the combustion in the furnace of the gas and atmospheric air now customarily supplied. Using good producer gas and air (about excess), vboth preheated in the regen- 40 erators to around 1000-C., the maximum combustion temperature will generally approximate 2100 C5 Although the flame is directed toward the bottom of the furnace, the temperature of the roof always exceeds that of the fused chargeor bath,

due to the high capacity of the latter for absorbing heat. Thus when the temperature of the bath is 1600 (1., that of'the roof a will ordinarily be 1700 C. or more. Silica brick will not stand a higher temperature.

This condition results 1n other serious-disadvantages besides that of preventing 1ncrease of-combustion temperature in the furnace. There is, for example, every great actory which loss of heat by radiation from the roof. It is lmpractical to prevent this b insulation, because the retained heat woul be destructive.

I have discovered that these difficulties may be avoided by assing a current of a suitable gas along t e under side of the roof. This. gas should be preheated, or should be combustible in part, or both, in order that the'eifective temperature of .the

FEILD, .O'F J'ACKSON HEIGHTS, NEW YORK, ASSIGNOR T0 THE LINDE furnace may not be materially lowered.

Various gases or gaseous mixtures may be used. A particularly advantageous procedure is to work the open hearth process, 9.0-

cording to the present invention, :with atmospheric air treated to produce two'ifractlons containing respectivel a greater and a less proportion of oxygen tli Both these fractions will preferably be preheated by passing through regenerators containing the usual checkerwork or the like.

The high oxygen fraction is used with producer as, oil, or other suitable combustible to pro uce a bath temperature hitherto considered to have a disastrous effect upon the furnace roof and checkerwork. The low oxygen fraction is passed in. a stream below the roof, and being at a considerably lower temperature than the bath or the high temperaan exists in'air;

ture flame at the surface of the bath, it abstracts heat from the roof and carries it off, thereby limiting the temperature which the roof can attain. At the exit ports the two gas streams unite, so that the temperature to which the checkerwork is.subjected is kept within practical bounds.

.The low-oxygen fraction will ordinarily be supplied together with a combustible gas oil, or the like, so that heat willbe generate by the rotective gas current sweepin the roof. owever, the term low-oxygen includes gases containing little or no oxygen. When such gases are used, the preheating should be adequate to prevent an objectionable reduction of the furnace temperature.

Illustrative embodiments of the invention are. illustrated in the accompanying. drawing, in whicha Fig. 1 is a somewhat diagrammatic vertical section through half of an open-hearth furnace and its regenerators;

Fig. 2 is a section on line 11-11 'of'Fig. 1; and

rangement.

Fig. 3 is a diagram'of a modified port ar- 2 7 numeral 1 denotes a furnace of conventional type having a hearth 2 and regenerators 3, 4,

and 5, suitably connected with the gas and air supply, not shown. As noted on Fig. 1, the regenerators are adapted to serve respectively for the preheating of fuel gas, low-oxygen gas, and air or oxygenated air. Uptakes 6 and 7 conduct the comburent gases from regenerators 1 and 5 to inlet ports 8 and 9, respectively. These ports are directed so as to send one gas stream toward the bath and another toward the roof. The fuel gas is fed into the-furnace from regenerator 3 by uptakes (notshown) leading to ports 10 and 11, 12 and 13 (Fig. 2). It will be understood that these ports are directed as are their corresponding ports 8 and 9.

The relative amounts of fuel gas and comburent may be adjusted by suitably proportioning the cross-sectional area of the uptakes. Figs. 1 and '2 of the drawing illustrate one practical embodiment, but the invention is not limited to the arrangement or proportions shown. may necessitate a marked increase or decrease in capacity .of one or more of the inlets to the furnace. p

In Fig. 3 an alternative arrangement of ports is shown. In this, the fuel gas is fed through a central passage 14 divided by a partition 15 which is flared at the end ad.

jacent to the furnace'so that one portion of the as stream is deflected upwardly and the ot er downwardly. The comburent gases (preferably oxygenated air and aircontaimng an increased proportion of nitrogen) are fed respectively through passages 17 and16. p

The flow of gases will be reversed in the usual manner, entering from the opposite end of the furnace, which is identical with that illustrated. If necessary, suitable} dampers may be provided to secure a proper distribution of the furnace gases to the three regenerators.

. It will be apparent that in both forms of furnace illustrated, the low-oxygen gas and its combustible sweep the under side of the furnacev roof, thus protecting 'it from the materially higher temperatures prevailing in the lower part of the furnace. The oxygen content of the air fractions may be adjusted as desired, provided the maximum heat of combustion p'roduced by the lowoxygen gas is substantially less than that which would cause failure" of'the roof. Since the cooling gas introduces a large amount of heat, either as sensibleheat, or heat of reaction,,or both, the furnace processes are-not interfered with..

Air separated into two fractions containing respectively 30% and 18% of oxygen by weight may be advantageously used. Various other proportions are also suitable.

Special conditions The gases used in the process may be prepared in any desired way, but the fractionation of air affords a cheap and convenient source.

Important improvements in the open hearth process and other high temperature operations are produced by the use of a protective gasin accordance with the present invention. Among these improvements may be mentioned the reduction of the time for reaction, utilization of low grade fuel gas, and the oxidation of materials not readily worked with the present flame of relatively low oxidizing power.

The present process may be used, with or without modification, in a number of connections other than those specifically 'de- 7 scribed herein, and the invention is therefore defined broadly in the appended claims.

I claim: I

1. Process of conducting high temperature furnacing operations, comprising passing a hot gas, of lower temperature than the main reaction zone of the furnace, between such zone and a portion of the furnace liable to failure from excessive heatmg.

2. Process of conducting high temperature furnacin operations, comprising passing a combusti le gas and a gas containing oxygen in lower proportion than that in atmospheric air, between such zone and a portion ofthe furnace liable to failure from excessive heating. .1

3. Process of conducting high temperature 100 furnacing operations, comprising generating a high temperature in the reaction zone of the furnace, and passing a hot gas of relatively. lower temperature along the inner surface'of the roof of such zone.

. 4. Process of conducting high temperature 'furnacing operations, comprisin passing a gas containing a higher proportion of oxygen thanatmospheric air into the reaction zone-of the furnace to produce a temperature therein which would normally be destructive to a portion of the furnace wall, and protecting such portion by causing a hot gas of relatively lower temperature to swee over its inner surface.

5. rooess of working furnaces of the open-hearth type, comprising utilizing. a gas rich in oxygen to produce a hearth temperature in excess of that obtainable by combustion involving air, and preventing the .120 adverse effects of heat upon the furnace roof by passing a hot gas of lower temperature in contact with the inner surface of the roof.

' 6. Process of working furnaces of the openhearth type,.comprising utilizing a gas rich in oxygen to produce a hearth temperaturein excess of that obtainable by combustion involving air, and preventing the adverse effects of heat-upon the furnace roof by passing a fuel gas in admixture with a lowoxygen gas in contact with the inner surface of the roof.

7. Process of working furnaces of the openheaith type, comprising heating the hath by burning a fuel gas with a gas containing oxygen in greater proportion than that in atmospheric air, and passing inconteet with the inner surfziceofthe furnace roof at preheated combustible gas and a pre- 10 heated low-oxygen gas, whereby the roofis shielded from the destructive action of heat from. the bath.

In testimony whereof, Ieflix by signature.

ALEXANDER L. FEILD. 

